1. Field of the Invention
This invention relates generally to continuous hot rolling mills for so-called "long" products such as bars, rods, and the like, and is concerned in particular with an improved method and apparatus for rolling concrete reinforcing elements.
2. Description of the Prior Art
As disclosed for example in U.S. Pat. No. 4,953,379 (Richartz), it is know to employ two successive two roll passes to roll round bars into concrete reinforcing elements having circular core cross sections with protruding ribs or fins. In U.S. Pat. No. 3,641,799 (Wildt), a similar arrangement is employed to roll indentations into the bar, the resulting product again having a circular core cross section. Because of their circular core cross sections, such products are subjected to relatively high bending stresses. They also exhibit a tendency to twist when being formed into structural shapes in automatic so-called "stirrup" machines. Moreover, where the roll passes used to roll the circular cross sections are defined by conventional grooves, the process of grinding the notches which form the rebar ribs into the grooves is difficult, time consuming, and expensive. The conventional grooves are also prone to rapid wear because of pronounced forward slip.
As disclosed in U.S. Pat. No. 1,458,381 (Baehr) and U.S. Pat. No. 4,034,587 (Schwarz), it is also known to roll reinforcing bars with either circular or square core cross sections using single four roll passes. The rolling of reinforcing bars with round core cross sections results in the disadvantages noted above. Moreover, the rolls of four roll passes require precise adjustment, and are necessarily dedicated to the rolling of only one product size. Thus, normal wear and/or changes in product sizes will necessitate frequent mill shut downs to accommodate roll changes. U.S. Pat. No. 3,214,877 (Akin) teaches the rolling of square or round bars into flat sided and ribbed process sections which can then drawn through dies to produce the finished products. This method is labor intensive and unduly expensive.
An objective of the present invention is to obviate the drawbacks and disadvantages of the prior art by providing an improved two-roll, two-pass method and apparatus for hot rolling round bars into reinforcing elements having flat sided cores with ribs or the like protruding from the flat sides thereof. The cores will typically be a square, but other shapes including for example, rectangles, are also possible.
A companion objective of the present invention is to produce the aforesaid ribbed flat sided corse by taking only modest reductions on the order of 10-15% in each successive roll pass, thereby reducing groove wear and prolonging useful roll life.